The Cave Bath at Miskolctapolca, Hungary. From Wiki Travel: A large cave system, which has water temperatures from 20-36 Celsius (thermal water), and has warm, wet air inside even in the winter. The caves are around 150 meters long but naturally nothing is straight, and it's all quite dark (it's a cave, after all). The bath also has pools outside the cave. The Cave Bath is surrounded by a large park which has an artificial lake where you can row boats.